Heat oil in a medium size soup pot and sauté onion with a pinch of salt until translucent and about 5 minutes. Then add the garlic and sauté until fragrant.
Add the lentils, half the water and bay leaves cover and bring to a boil.
Simmer lentils for about 20 minutes until they begin to soften.
Add the carrots, potatoes, remaining water (or just enough water to cover the vegetables) and a generous pinch of salt and simmer covered another 20 minutes until vegetables are cooked through.
Turn off the heat and add in the spinach leaves, stirring until they wilt (this will take a minute or two). If using kale, these leaves are tougher and will need to be put in the soup the last 5 minutes of cooking.
Season to taste with additional salt and some freshly ground pepper. Add in some fresh thyme if desired.